Cyclo(-RGDfK) is a potent and selective inhibitor of integrin αvβ3 with IC50 of 0.94 nM. Cyclo specifically targets tumor microvasculature and cancer cells by binding to αvβ3 integrin on the cell surface.

αvβ3:0.94 nM.

Cyclo (-RGDfK-) has a high affinity for purified integrin (Kd: 41.70 nM). It is reacting with HEK293(β3) cells moderately. The micelles modified by Cyclo(-RGDfK-) show strong affinity to T-24 cells and strong inhibitory effect on the proliferation of T-24 cells.

In athymic mice bearing α(v)β(3)-integrin-positive C6 gliomas, Cyclo (-RGDfK-) modification induces less tumor metabolic activity, less tumor progression, fewer intratumoral vessels.

Isolated Integrin Binding Assays.:Purified integrin (1 μg/mL; 4℃) is used to coat 96-well microtitre plates, which are then blocked with bovine serum albumin (BSA) (3% in 1 mM CaCl2, 1 mM MgCl2,10 pM MnCl2, 100 mM NaC1,50 mM Tris-hydroxymethyl-aminomethane; pH 7.4), and incubated (3 h at 30 ℃) with biotinylated ligands (1 pg/mL in binding buffer: 0.1% BSA, 1 mM CaCl2,1 mM MgCl2, 10 μM MnCl2, 100 mM NaCl, 50 mM Tris-hydroxymethyl-aminomethane; pH 7.4) in the presence or absence of serially diluted peptides. After washing (3×5 min with binding buffer), the bound biotinylated ligand is detected with alkaline-phosphatase conjugated goat anti-biotin antibodies (1 μg/mL; 1 h, 37℃), using p-nitrophenyl phosphate as chromogen. Cyclo (-RGDfK) binding in the absence of competitor is defined as 100% signal; binding to blocked wells in the absence of integrin is defined as 0%. Concentrations of Cyclo (-RGDfK) required for 50% inhibition of signal (IC50 values) are estimated graphically.